Photoprint developing apparatus and method

ABSTRACT

Imagewise exposed photocopy sheets bearing electrostatic charge patterns are developed with an electrically conductive &#39;&#39;&#39;&#39;one component&#39;&#39;&#39;&#39; toner by driving each sheet downwardly into and through a mass of the toner powder held in a container space, along a path therein between a lower sheet guiding structure extending partially within and partially outside the powder mass and an electrically conductive organ that has a cylindrical peripheral outline regularly profiled as viewed in circumferential direction, is partially immersed in the powder mass, and is rotated in the direction of the sheet movement at a peripheral speed at least approximately equal to the speed of the sheet. The sheet leaving the powder mass is guided upwardly for engagement by means which drive it out of the powder container, and as it moves upward it is mechanically vibrated, as by high speed impacts of a polygonal rotor, to remove loosely clinging powder particles.

United States Patent [191 lfiratcoski et a1.

1451 Mar. 11, 1975 1 PHOTOPRINT DEVELOPING APPARATUS AND METHOD [75] Inventors: Francis L. Kratcoski, Lincolnshire,

111.; Adrianus H. Willemse, Grubbenvorst, Netherlands [73] Assignee: Oce-van der Grinten N.V. Venlo,

Netherlands [22] Filed: June 26, 1974 [21] Appl. No.: 483,319

[52] U.S. C1 ..118/637,117/17.5, 355/3 DD, 355/17 [51] Int. Cl G03g 13/08 [58] Field of Search 118/637; 117/175; 355/3 DD, 17

[56] References Cited UNITED STATES PATENTS 2,919,672 l/l960 Benn et a1 118/637 2,972,331 2/1961 Limberger l 118/637 2,972.332 2/1961 Limberger 118/637 3,263,234 7/1966 Epstein et a1. 118/637 Primary ExaminerMervin Stein Assistant Examiner-Douglas A. Salser Attorney, Agent, or Firm-Albert C. Johnston [57] ABSTRACT lmagewise exposed photocopy sheets bearing electrostatic charge patterns are developed with an electrically conductive one component toner by driving each sheet downwardly into and through a mass of the toner powder held in a container space, along a path therein between a lower sheet guiding structure extending partially within and partially outside the powder mass and an electrically conductive organ that has a cylindrical peripheral outline regularly profiled as viewed in circumferential direction, is partially immersed in the powder mass, and is rotated in the direction of the sheet movement at a peripheral speed at least approximately equal to the speed of the sheet. The sheet leaving the powder mass is guided upwardly for engagement by means which drive it out of the powder container, and as it moves upward it is mechanically vibrated, as by high speed impacts of a polygonal rotor, to remove loosely clinging powder particles.

16 Claims, 4 Drawing Figures mmm um I 870017 SHEET 1 [1f 2 PATENTEDKARI H915 3.870.017

' SHEET 2 p 2 lu\ l PHOTOPRINT DEVELOPING APPARATUS AND METHOD This invention relates to an apparatus and method for developing photoprints by inductive attraction of an electrically conductive developing powder, or toner, to an electrostatic charge pattern on a support being moved through a mass of the powder.

In a known type of such apparatus, as described in Netherlands Patent application No. 72 14704 and shown especially in FIGS. 1 and 7 thereof, a quantity ofthe developing powder is held in a container and the support, such as a sheet of paper, is transported along a path that extends through the mass of powder and is limited by lower and upper guides situated partially in and partially out of the powder mass.

In that known apparatus the support is brought into the developing powder between the two guides by a first pair of rollers which push it through the powder, and then its leading edge is gripped by a second pair of rollers which pull it out ofthe powder mass. This movement of the support pushes some of the developing powder toward the side of the container where the support exits. Consequently, as the photocopying work continues, the powder become unevenly distributed in the container, apowder-free zone being created at the support entry side of the container while powder accumulates at the exit side. This on the one hand results in the adherence and development of powder on areas of the support where no charge is present, so that an objectionable background is formed, and on the other hand, it gives rise to a friction effect by which developing powder already deposited on the charged image areas of the support tends to be scraped away so as to leave an incompletely developed image.

The object of the present invention is to provide a developing apparatus which, in general, is of the known type mentioned above but by which the stated disadvantages of the known apparatus are largely or entirely avoided.

According to the present invention, the upper of the guides which limit the path of movement of the support through the mass of powder in a powder container is constituted by a rotatable organ made of electrically conductive material, which has a cylindrical peripheral outline that is regularly interrupted, or profiled, as viewed in circumferential direction, and this organ is rotated so as to move its periphary in the direction of the movement of the support through the powder.

As a result of the rotation of the profiled organ, the developing powder tending to accumulate at the exit side of the container is continually worked away from there, due to quantities of the toner being continually displaced by the peripheral profiles from the exit side toward the entry side of the container. Thus, a sufficiently even distribution of the developing powder is maintained in the container. Further, by virtue of the conductivity of the profiled organ and its extensive contacts with the powder in the container near to the charged surface of each support passed through the powder mass, the organ readily dissipates secondary electrostatic charges which tend to be induced in particles ofthe powder away from the charge pattern on the support. In this way it keeps the powder mass in a desired neutral, or uncharged, condition.

The invention is especially suited for the development of electrostatic images by the use of a so-called one-component electrically conductive toner, the particles of which are attractable by electrical inductance to the charged image areas of the copy sheets being passed through the powder container. Such a toner, which may be made, for instance, as described in Netherlands patent applications Nos. 72 07688 and 72 14704, is particularly suitable for this use when made with a specific resistance of between 10 and I0 ohms. cm. and, for example, with a number average particle size of about 20 and 25 microns. A toner ofthis nature. being kept in substantially neutral condition in the powder container, exhibits little tendency to adhere to the uncharged areas of the copy sheets. To the extent that particles of the toner do cling loosely to uncharged areas of a sheet emerging from the powder mass, these particles are removed satisfactorily, so as to prevent the fixing of an objectionable background to the sheet, by subjecting each sheet to mechanical vibrations, as by striking it with corners of a rotor having a polygonal surface rotated at high speed, while it is being drawn upwardly away from the powder mass at the exit side of the container.

The rotation of the profiled organ desirably is effected by driving it at a peripheral speed at least approximately as great as the speed of movement of the copy sheet through the developing powder. Its speed can be as high as about twice the transport speed of the sheet. The movement of the profiled organ, by displacing some of the powder near to its peripheral profiles, facilitates the movement of the copy sheet through the powder mass. The profiles ofthe rotatable organ generally are constituted by a plurality of elongate formations, such as ribs or strips, which are spaced apart circumferentially at the periphery of the organ and preferably extend substantially parallel to its axis of rotation.

According to one embodiment of the invention, the organ comprises a generally cylindrical body having fixed thereto a plurality of rib-like strips which are spaced apart circumferentially at its periphery and extend parallel to its axis. In a modification, the cylindrical body is provided with one or more of such strips extending spirally over its periphery.

According to a further development of the invention, the periphery of the organ is constituted substantially entirely by a circular series of slender strips, or bars, which extend substantially parallel to the axis of rotation and are spaced apart circumferentially thereof. These strips are fixed about a supporting shaft to form a kind of cage wheel that is open for free movement of the powder through the spaces between the strips, and which continually agitates and displaces the powder in the container so as to keep the powder mass evenly distributed, fluffy and loose.

Other features and advantages of the invention will become apparent from the following description and the accompanying drawings of illustrative embodiments thereof. In the drawings:

FIG. I is a schematic cross-sectional view ofa developing apparatus according to one embodiment of the invention, in association with an apparatus for fixing the developed images;

FIG. 2 is a perspective view of the rotatable organ consitiuting the upper guide for sheets passed through the developing section, or powder container, of the apparatus of FIG. 1',

FIG. 3 is a schematic cross-sectional view of the developing apparatus according to a further embodiment of the invention; and I FIG. 4 is a perspective view of the rotatable organ constituting the upper sheet guide in the apparatus of FIG. 3.

The apparatus represented in FIG. 1 is intended for use as the developing and fixing sections of an electrostatic photocopying machine by which suitable supports in sheet form, such as an electrophotographic paper sheet 1 having a photoconductive surface la, are fed downwardly into the developing section, one after another, after having been electrostatically charged and then imagewise exposed for the formation ofa developable electrostatic charge pattern, or latent image, on the photoconductive surface. Reference is made to U.S. Pat. Nos. 3,700,326 and 3,700,327 for particulars of one type of photocopying machine for which this apparatus is suitable.

After being imagewise exposed, the copy sheet is driven between rollers 41 and 42 and via stationary guides 50, 51 and a lower pair of driven rollers 52, 53 into the developing section of the illustrated apparatus.

The developing section 10 comprises a container having a contoured body wall 60 for holding a mass of the developing powder. Wall 60 has a concave, preferably'substantially semi-cylindrical, bottom portion 66 which, at the side where the copy sheet is introduced, is lengthened by an obliquely upwardly extending portion 67 and at the other side, where the support exits from the powder mass, is provided with an upward extension 66a from which a partition 68 slopes backward and then upward to form a recess facing the path of the copy sheet. This recess accommodates a mechanism for removing loose powder from the copy sheet, as to be described below.

The contoured wall 60 of the container may be formed by bending a rectangular metal plate into the desired shape or by extrusion or molding of a metal or a resin composition. It is closed off by a plate at each end so that the developing powder cannot escape laterally. The container wall 60 is supported between two rods 61 and 62 which extend between two frame plates, one of which is shown at 63, and are removably fixed to these plates, for instance by screws.

In the embodiment of FIG. l,'a plurality of parallel guide ribs 64 are arranged against and along the inside of the container body wall 60. These ribs follow the contour of that wall along its entry extension 67 and its arcuate bottom portion 66, and at the exit side they extend obliquely upward across the recess formed by partition 68. The guide ribs 64 are made of or coated with a non-conductive material having a low coefficient of friction, such as polytetrafluoroethylene, to facilitate sliding movement of the support through the container.

According to the invention, a profiled organ 65 rotatable in the direction of movement of the copy sheet is arranged inside the container 60 as an upper, path limiting means spaced a suitable distance away from the lower guide ribs 64 in the powder holding portion 66 of the container. The organ 65 is made of electrically conductive material and, in this embodiment, comprises a generally cylindrical body the peripheral surface of which is provided with profiles 69 regularly spaced apart in the circumferential direction. These profiles consist of a number of elongate strips or elevations, in this instance four elevated ribs 69, which extend parallel to the axis of the cylindrical body. These ribs are formed, for instance, by fixing metal strips on the surface of the cylindrical body; for example, copper wires are soldered to its surface. It is to be understood, however, that various other forms of profiling may be utilized, including grooves formed in and along a cylindrical body, either parallel to its axis or spirally over its surface, or elevated strips extending spirally over its surface, or combinations of such grooves and strips.

The ends of. the cylindrical organ are provided with journals a and 65b which are freely rotatable in bearings in the frame plates, and one of these journals is connected with a driving mechanism (not shown) by which it is rotated at a speed giving the organ 65 a pcripheral speed at least approximately as great as the transport speed of the copy sheet. Its speed may be as high as about twice the transport speed. The rotation of the organ with resulting movement of powder along the path of its profiles facilitates the movement of the copy sheet through the developing powder.

A covering plate 70 is mounted above the powder holding space of the container on supports 71 which are fixed against the frame plates by screws..A skirt portion 70a of this covering plate 70 and the extension 67 of the container wall 60 form between them a narrowing passageway 2 for the introduction of the copy sheet, in such manner that powder is prevented from escaping at that side of the container. If desired, a second container holding a reserve supply of the developing powder may be installed in the space between the organ 67 and the upper portion of plate 70, to be used for replenishing the powder in the working space of container 60.

The background suppressing mechanism arranged at the exit side of the container 60 comprises a rotor 72 having a polygonal periphery, in this case one of triangular cross section, which is rotatable in bearings mounted in the frame plates and is driven at a high speed counter-clockwise (as viewed in FIG. 2) by any suitable motor or transmission. The rotor 72 is mounted in bearing so located that its corners 72a, i.e., the tops of the triangle, move beyond the upward extensions 64a of the guide ribs 64 into the path of the copy sheet moving upwardly out of thepowder container, whereas the flat sides of the rotor do not intrude into the path of the'copy sheet. Since in this embodiment there are several of the guide rib extensions 64a, the rotor 72 preferably comprises a plurality of the polygonal elements spaced apart on its shaft so that each guide rib lies in a space between two of these rotor elements. The high speed rotation of the rotor, for instance at about 900 r.p.m., causes its corners 72a, by striking the back side of each sheet rising out of the powder mass, to vibrate the sheet intensively so that powder particles adhering loosely to it are shaken off and will fall back into the powder mass.

the sheet out of the powder container. The guide mem ber 73 is made with an anti-friction surface, for instance being made of metal coated with polytetrafluorethylene.

It will be evident from the foregoing that each copy sheet 1, after having a charge pattern formed on it, is delivered downwardly into the powder container where the ribs 64 guide the leading edge of the sheet along the curvature of bottom portion 66 and then upwardly out of the powder mass and past the vibration rotor 72 to a location where the sheet is gripped by the rollers 76, 77 which pull it out of the powder container. Each sheet thus is transported through the developing powder with the charge pattern on its surface la disposed at a limited distance away from the periphery of the rotating organ 65. Some of the powder particles are attracted and adhered by electrostatic forces to the charged image areas of the sheet. The powder particles which may cling mechanically to other areas of the sheet, such as by reason of Van der Waals forces or of the roughness of the sheet, are sufficiently loose that they are shaken off by the vibrations imparted to the sheet as it is moved past the rotor 72.

The rollers 76, 77 deliver the developed copy sheet from the developing section into the fixing section 12 of the illustrated apparatus. These rollers may have metal surfaces, and the roller 77, which comes into contact with the powder image of the copy sheet, is provided with a cleaning device 100. The cleaning device may simply be a scraper that will scrape away any powder transferred to the roller 77 so that this powder will fall back into the powder container--for instance, a Melinex strip mounted in a metal setting fixed to the side frames may be pressed against roller 77 at an angle of about 30. in the embodiment shown the cleaning device 100 is a felt cushion 101 fixed on the end ofan arm 102 which is connected with a freely rotatable bar 103 so that the cushion 101 may be pressed sufficiently against the roller 77 by gravity or by a spring.

The fixing section 12 as shown comprises a so-called contact fixing apparatus whereby the copy sheet carrying the powder image is transported between two moving surfaces forming a nip, at least one of which is heated so that the copy sheet takes up enough heat from the heated surface to soften the powder, which is thermoplastic, and cause it to be fixed in place on the sheet when the sheet cools. The invention, however, is not limited to this type of fixing apparatus, as various other fixing devices can be used, for instance, devices for fixing the image by pressure or fixing devices in which the thermoplastic powder is softened by heat radiation or by solvents.

In the fixing section 12, the first moving surface is formed by a hollow rotary drum 80 which has a relatively thin, heat-conductive cylindrical wall made, for instance, of copper or aluminum. The drum 80 is provided with internal heating means (not shown), which may be an infra-red heater but preferably is an electrical heating coil arranged inside the drum. The outer surface of the drum is preferably provided by a thin coating or layer of an anti-adhesive material, such as polytetrafluoretheylcne or silicon rubber.

The second moving surface of the fixing section 12 is formed by an endless belt 90 which is trained about two rollers 91, 92 and a guide 93 so that a flight of the belt 90 extends about and bears against a major portion of the circumference of drum 80, for instance covering an angle ofmore than 180. The endless belt 90 may be made of a heat-resistant fabric coated with silicon rubber on its side engaging the drum 80, or may be made of a silicon rubber containing a suitable filler.

Each of the rollers 91 and 92 comprises a metal core covered by a rubber sleeve and is mounted to rotate freely in bearings in the frame plates of the apparatus; and roller 92 is rotated by a suitable mechanism not shown. The guide 93 comprises a metal base covered by a layer ofa material having a low coefficient of friction, such as polytetrafluoroethylene, and is mounted non-rotatably between the frame plates so that the belt slides over the curved surface of guide 93. Each end of that surface is bounded by a curved flange 94 lying close to the adjacent edge of the belt 90.

A scraper 95 bearing against the outer surface of drum 80 serves to loosen the copy sheet from the drum. The scraper shown comprises a Melinex" strip disposed at an angle of about 25-30 against the surface of the drum 80 and having a concave profile along which the copy sheet is guided from the drum toward a tray for receiving the copies produced. Further, a cleaning device is provided for removing any powder particles adhering to the drum 80. This device comprises a roller 106 having a metal core about which a sleeve of highly absorbtive material, for instance paper or felt, is arranged, and which is rotatably mounted in bearings in the ends of two parallel lever arms 107 which can pivot about the axis of a skaft 108 fixed between the frame plates.

The copy sheet is conveyed to the belt 90 via the rollers 76, 77 and is gripped and transported between the belt 90 and the drum 80, with the powder image coming into contact with the belt 90. The copy sheet is heated by drum 80 so that the powder image partially melts, after which the copy sheet is delivered to the recciving tray via the scraper 95. The powder image is fixed on the copy sheet upon cooling. With this method, additional pressure can be applied to the sheet as it passes between the drum 80 and roller 92, in order to obtain a smoother copy.

1n the arrangement shown in FIG. 1, the fixing apparatus together with the roller pairs 52, 53 and 76, 77 and the guides 50, 51 are mounted between their own side frame plates, one of which is shown at 14, so that the whole fixing section can be slid as a unit laterally into and out of a recess of appropriate size formed in the side frame plates of a photocopying machine. The elements of the developing section 10 also are mounted between two separate frame plates, one of them being shown at 63, which fit into a recess, such as the cut-out area 15, formed in the frame plates of the fixing apparatus; so the developing apparatus also can he slid as a unit into and out of its working position in the copying machine. Further, a heat-insulating panel 110 is placed between the fixing section 12 and the developing section 10, and another heat-insulating panel may be provided over the whole assembly, in order to limit heat transfer from the fixing apparatus to the developing apparatus and other parts of the copying machine.

The developing apparatus according to the invention as illustrated in FIG. 3 of the drawings is embodied in a developing section 101 adapted for use in an electrostatic photocopying machine of the type described above. The parts of section 1011 are assembled as a unit between two mating side frame plates, one of which is shown at 163.

Each sheet 1, carrying an electrostatic charge pattern to be developed on its surface 11, is fed downwardly into the developing section by rollers 141, 142. The sheet passes between stationary guides 150, 151 into the nip of two rollers 152, 153 which drive it downwardly through a narrowing entry passageway 2a into and through the powder holding space 2b of the powder container and thence upwardly away from that space in an exciting path extending over a wall opening 162 to a series of transport rollers 176, 177, 178, 179 and 180. Rollers 177, 178, 179 and 180 bear against the surface of the larger support roller 176, which is driven synchronously with the roller pairs 141, 142 and 152, 153. Thus, the sheet while being driven out of the developing section is turned into a lateral direction of movement for engagement by the fixing apparatus (not shown) of the photocopying machine. A scraper blade 177a bears against the surface of the roller 177 to remove any powder collected on it from the imagebearing surface of the sheet.

The powder container in this embodiment is defined bya contoured body wall 160 held in between the side frame plates of the developing section. This wall has a substantially semi-cylindrical bottom portion 166 in which the mass of developing powder collects and from which an extension 167 rises at an inclination so as to form one border of the sheet entry passageway 2a, the opposite border of which is formed by a skirt portion 170 a of a cover plate 170 located above the powder space in thecontainer.

At the other side of bottom portion 166, where the sheet exits from the powder mass, the wall 160 has a substantially vertical upward extension 161 in which opening 162 is formed, and which leads each sheet into the nip of the rollers 176, 177 while a trailing portion of the sheet is still being driven by the rollers 152, 153. A sloped plate 173 or other suitable guide means is arranged opposite the upper portion of wall extension 161 to keep the leading edge of each sheet in the desired exiting path.

The inner surface of the contoured body wall 160 in FIG. 3 itself serves as the lower guide defining the path of movement of each sheet through the powder. The

wall 160 accordingly is made of a dieelectric material and with a smooth inner surface along which the leading edge and the body of each sheet will slide with little frictional resistance as the sheet is fed into the container by the rollers 152, 153. For instance, wall 160 may be made by extrusion or as a molding of an acrylonitrile-butadiene-styrene resin.

A wall 168 which slopes backwardly and upwardly from wall extension 161 so as to enclose the opening 162 forms a laterally recessed portion, or chamber, of the container containing a triangular rotor 72 similar to the corresponding element in the embodiment of Fig. 1. The corners 72a of this rotor, which is driven at a high speed as previously described, move through the opening 162 so as to strike the sheet being moved out of the container and vibrate it so intensely that particles of the developing powder clinging loosely to the sheet are shaken off and will fall back into the powder space of the container.

The electrically conductive profiled cylindrical organ 165 according to the embodiment of FIG. 3 is formed as a kind of cage wheel. This organ has a conductive metal shaft 190 mounted for rotation in the frame plates of the developing section 10a. End plates 191 and 192 and a central plate 193 on the shaft 190, and each made of electrically conductive metal, support a circular series of slender strips, or bars, 194 which extend parallel to its axis and are spaced apart circumferentially thereof. The strips or bars 194 may be lengths of a conductive metal rod or wire stock, for example, of copper wire of about 2 mm. in diameter. A sufficient number of these strips in circular arrangement, for example, about sixteen of them in the embodiment shown, forms the cylindrical outline and the peripheral profiles of the rotating conductive organ.

The bearings of the shaft 190 are so located in the frame plates that approximately a half ofthe circumference of organ is immersed in the mass of powder held in the concave bottom portion 166 of the powder container. The spaces between and inside the peripheral strips 194 permit the powder mass to lie and be displaced both inside and outside the orbit of the organ, which assists in keeping the powder well agitated and loose, as well as evenly distributed, during the rotation of the organ. Furthermore, the peripheral strips 194, by moving through the powder mass at a limited distance away from the charged surface of each sheet being passed through the powder, take up and conduct away errant electrostatic charges which are induced in particles of the powder that lie near but are not attracted to the charged image areas of the sheet.

It is to be understood that the invention is not restricted to the particular embodiments described and illustrated and that numerous'modifications can be introduced without departing from the substance of the invention.

We claim:

1. An apparatus for developing an electrostatic charge pattern on a support sheet by inductive attraction thereto of particles of an electrically conductive developing powder, including a container for holding a mass of said powder and having therein lower and upper means extending partially within and partially outside the space occupied by the powder and spaced apart therewithin to define a path for movement of the sheet through the powder mass, and means for transporting the sheet into and along said path and thence out of said container, the improvement which comprises said upper means being constituted by an electrically conductive organ having a cylindrical peripheral outline that is regularly profiled as viewed in circumferential direction, said organ being rotatable to move its periphery in the direction ofthe movement ofthe sheet through said path so that its profiles will displace powder from the sheet exit region of said space toward the sheet entry region thereof.

2. Apparatus according to claim 1, the profiles of said organ comprising a plurality of elongate strips spaced apart circumferentially at its periphery and extending substantially parallel to its axis.

3. Apparatus according to claim 1, said organ comprising a generally cylindrical body having a plurality of elongate ribs spaced apart circumferentially on its peripheral surface and extending substantially parallel to its axis.

4. Apparatus according to claim 1, said organ comprising a generally cylindrical body having at least one elongate rib extending spirally over its peripheral surface.

5. Apparatus according to claim 1, and means for rotating said organ at a peripheral speed at least approximately equal to the transport speed of said sheet.

6. Apparatus according to claim 1, and means for rotating said organ at a peripheral speed up to about twice the transport speed of said sheet.

7. Apparatus according to claim I, said container comprising a concave bottom portion to hold the powder mass and means for guiding downwardly into and along the curvature of said bottom portion, and thence in an upward path leading out of the container, a sheet fed thereinto by said transporting means, said organ being mounted with the lower portion of its circumference disposed in the space of said bottom portion at a limited distance away from the peth of a sheet moving therethrough.

8. Apparatus according to claim 1, said container comprising means for guiding the sheet out of the container in an upward path extending above said powder space, and means for vibrating the sheet as it is moved along said upward path-so that particles of the developing powder clingly loosely to the sheet will be shaken off to fall back into the powder space.

9. Apparatus according to claim 8, said means for vibrating the sheet comprising a rotor having a polygonal peripheral surface and mounted for rotation so as to bring the corners of said surface successively into and out of said upward path, and means for rotating said rotor at a speed sufficient to vibrate the sheet moving in said upward path by impacts of said corners against the sheet.

10. Apparatus according to claim 1, said container having a contoured body wall forming a substantially semi-cylindrical concave botton portion to hold the powder mass, an oblique upward extension of said bottom portion at one side thereof for guiding downwardly into and along the curvature thereofa sheet fed thereinto by said transporting means, and an upward extension at the other side thereof for guiding said sheet into an upward path extending above said space and leading out ofthe container, said organ being mounted with approximately the lower half of its circumference disposed in the space of said bottom portion at a limited distance away from the path of a sheet moving therethrough, said container further having a recessed portion offset laterally from and opening toward said upward path, a rotor having a polygonal peripheral surface mounted for rotation in said recessed portion so as to bring the corners of said rotor surface successively into and out of said upward path, and means for rotating said rotor at a high speed sufficient to shake loose particles of said powder from the sheet moving in said upward path by vibratory impacts of said corners against the sheet.

11. Apparatus according to claim 10, said rotor surface being triangular in cross section.

12. A method of developing electrostatic charge patterns on imagewise exposed photocopy sheets, which comprises driving each sheet downwardly into and through a mass of electrically conductive developing powder held in a container space, along a path between a lower, stationary sheet guiding structure extending partially within and partially outside said mass and an electrically conductive organ that has a cylindrical peripheral outline regularly profiled as viewed in circumferential direction and has the lower portion of its cir cumference immersed in said mass, continuously rotating said organ so that its periphery moves through the powder mass at a limited distance from the charged surface of the sheet and in the direction of movement of the sheet through said mass, thereby continually displacing powder from the sheet exit side toward the sheet entry side of said space, and guiding the sheet upwardly away from said mass and then driving it out of the powder container with particles of said powder held to the charged areas of said pattern by inductive attraction.

13. A method according to claim 12, said powder having a specific resistance of between 10 and 10 ohms. cm. and consisting of particles having a number average particle size of about 20 to 25 microns.

14. A method according to claim 12, the rotation of said organ being at a peripheral speed at least approximately equal to the speed of movement of said sheet through said mass.

15. A method according to claim 12, and as the sheet moves upward away from said mass subjecting it to mechanical vibrations so as to remove from it particles of said powder clinging to non-image areas of the sheet.

16. A method according to claim 12, and as the sheet moves upward away from said mass striking it with corners ofa polygonal surface rotating at a high speed suffieient to vibrate the sheet intensively and remove from it particles of said powder clinging to non-image areas of the sheet.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION Patent No. 3,870,017 Dated March 11, 1975 Francis L Kratcoski et al. Assignors to Oc-van der Grinten N.V. of

Venlo, Netherlands It is hereby certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet insert [30] Foreign Application Priority Data: June 28, 1973,

Netherlands 73.08994 Column 1, line 25, in place of "become" read becomes 7 line 48, in place of "periphary" read periphery Column 6, line 64, in place of "101" read 10 Column 7, line 2, in place of "11" read la line 9, in place of "exciting" read exiting Column 9, line 15, in place of "peth" read path 7 line 22, in place of "clingly" read cling Signcd and Scaled this fourth Day Of November 1975 {SEAL} A ttes t:

RUTH c. MASON c. MARSHALL DANN' ff" ("innmissiuner ofPatents and Trademarks ed as shown below:

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION Patent No. 3,870,017 7 Dated March 11, 1975 Francis L. Kratcoski et al. Assignors to Oc-van der Grinten N.V. of

Venlo, Netherlands It is hereby certified that error appears in the aboveidentified patent and that said Letters Patent are hereby correct- On the cover sheet insert [30] Foreign Application Priority Data: June 28, 1973,

Netherlands 73.08994 Column 1, line 25, in place of "become" read becomes line 48, in place of "periphary" read periphery Column 6, line 64, in place of "101 read 10a Column 7, line 2, in place of "11" read la line 9, in place of "exciting" read exiting Column 9, line 15, in place of "peth" read path line 22, in place of "clingly" read cling signed and Emailed this fourth Day of November-1975 O [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN' Arresting Officer (bmmissiuner nfParems and Trademark; 

1. An apparatus for developing an electrostatic charge pattern on a support sheet by inductive attraction thereto of particles of an electrically conductive developing powder, including a container for holding a mass of said powder and having therein lower and upper means extending partially within and partially outside the space occupied by the powder and spaced apart therewithin to define a path for movement of the sheet through the powder mass, and means for transporting the sheet into and along said path and thence out of said coNtainer, the improvement which comprises said upper means being constituted by an electrically conductive organ having a cylindrical peripheral outline that is regularly profiled as viewed in circumferential direction, said organ being rotatable to move its periphery in the direction of the movement of the sheet through said path so that its profiles will displace powder from the sheet exit region of said space toward the sheet entry region thereof.
 1. An apparatus for developing an electrostatic charge pattern on a support sheet by inductive attraction thereto of particles of an electrically conductive developing powder, including a container for holding a mass of said powder and having therein lower and upper means extending partially within and partially outside the space occupied by the powder and spaced apart therewithin to define a path for movement of the sheet through the powder mass, and means for transporting the sheet into and along said path and thence out of said coNtainer, the improvement which comprises said upper means being constituted by an electrically conductive organ having a cylindrical peripheral outline that is regularly profiled as viewed in circumferential direction, said organ being rotatable to move its periphery in the direction of the movement of the sheet through said path so that its profiles will displace powder from the sheet exit region of said space toward the sheet entry region thereof.
 2. Apparatus according to claim 1, the profiles of said organ comprising a plurality of elongate strips spaced apart circumferentially at its periphery and extending substantially parallel to its axis.
 3. Apparatus according to claim 1, said organ comprising a generally cylindrical body having a plurality of elongate ribs spaced apart circumferentially on its peripheral surface and extending substantially parallel to its axis.
 4. Apparatus according to claim 1, said organ comprising a generally cylindrical body having at least one elongate rib extending spirally over its peripheral surface.
 5. Apparatus according to claim 1, and means for rotating said organ at a peripheral speed at least approximately equal to the transport speed of said sheet.
 6. Apparatus according to claim 1, and means for rotating said organ at a peripheral speed up to about twice the transport speed of said sheet.
 7. Apparatus according to claim 1, said container comprising a concave bottom portion to hold the powder mass and means for guiding downwardly into and along the curvature of said bottom portion, and thence in an upward path leading out of the container, a sheet fed thereinto by said transporting means, said organ being mounted with the lower portion of its circumference disposed in the space of said bottom portion at a limited distance away from the peth of a sheet moving therethrough.
 8. Apparatus according to claim 1, said container comprising means for guiding the sheet out of the container in an upward path extending above said powder space, and means for vibrating the sheet as it is moved along said upward path so that particles of the developing powder clingly loosely to the sheet will be shaken off to fall back into the powder space.
 9. Apparatus according to claim 8, said means for vibrating the sheet comprising a rotor having a polygonal peripheral surface and mounted for rotation so as to bring the corners of said surface successively into and out of said upward path, and means for rotating said rotor at a speed sufficient to vibrate the sheet moving in said upward path by impacts of said corners against the sheet.
 10. Apparatus according to claim 1, said container having a contoured body wall forming a substantially semi-cylindrical concave bottom portion to hold the powder mass, an oblique upward extension of said bottom portion at one side thereof for guiding downwardly into and along the curvature thereof a sheet fed thereinto by said transporting means, and an upward extension at the other side thereof for guiding said sheet into an upward path extending above said space and leading out of the container, said organ being mounted with approximately the lower half of its circumference disposed in the space of said bottom portion at a limited distance away from the path of a sheet moving therethrough, said container further having a recessed portion offset laterally from and opening toward said upward path, a rotor having a polygonal peripheral surface mounted for rotation in said recessed portion so as to bring the corners of said rotor surface successively into and out of said upward path, and means for rotating said rotor at a high speed sufficient to shake loose particles of said powder from the sheet moving in said upward path by vibratory impacts of said corners against the sheet.
 11. Apparatus according to claim 10, said rotor surface being triangular in cross section.
 12. A method of developing electrostatic charge patterns on imagewise exposed photocopy sheets, which comprises driving each sheEt downwardly into and through a mass of electrically conductive developing powder held in a container space, along a path between a lower, stationary sheet guiding structure extending partially within and partially outside said mass and an electrically conductive organ that has a cylindrical peripheral outline regularly profiled as viewed in circumferential direction and has the lower portion of its circumference immersed in said mass, continuously rotating said organ so that its periphery moves through the powder mass at a limited distance from the charged surface of the sheet and in the direction of movement of the sheet through said mass, thereby continually displacing powder from the sheet exit side toward the sheet entry side of said space, and guiding the sheet upwardly away from said mass and then driving it out of the powder container with particles of said powder held to the charged areas of said pattern by inductive attraction.
 13. A method according to claim 12, said powder having a specific resistance of between 102 and 107 ohms. cm. and consisting of particles having a number average particle size of about 20 to 25 microns.
 14. A method according to claim 12, the rotation of said organ being at a peripheral speed at least approximately equal to the speed of movement of said sheet through said mass.
 15. A method according to claim 12, and as the sheet moves upward away from said mass subjecting it to mechanical vibrations so as to remove from it particles of said powder clinging to non-image areas of the sheet. 